=Dorsal Rami.=--The dorsal rami of the thoracic nerves are small and
supply the muscles and integument of the back. Each gives off a branch
directly dorsad to the spinal muscles, and a lateral branch which
reaches the integument some distance from the middle line.
=Ventral Rami.=--The ventral ramus of the first thoracic nerve enters
into the brachial plexus, as already described. The ventral rami of the
other thoracic nerves form the =intercostal nerves=. Each of these
passes ventrolaterad, lying close to the caudal border of a rib, in
company with the intercostal artery. Branches are given to the
intercostal muscles, and at about the middle of the length of the rib a
large lateral branch is given off, which passes to the more superficial
muscles of the thoracic wall (serrati posteriores, obliquus externus,
etc.), its main branches running dorsad and ventrad. The main
intercostal nerve extends ventrad to the transversus costarum and rectus
abdominis, supplying these muscles.
C. LUMBAR NERVES.--There are seven lumbar nerves, one passing from the
vertebral canal caudad of each lumbar vertebra.
=Dorsal Rami.=--The dorsal rami are similar to those of the thoracic
region, sending one branch dorsad to the muscles of the vertebral
column, another dorsolaterad to reach the integument at about the
lateral border of the longissimus dorsi. The dorsal rami are somewhat
smaller caudad.
=Ventral Rami.=--The last four lumbar nerves are interconnected to form
the =lumbar= or =lumbosacral plexus=. The first three are distinct, and
will therefore be described separately.
The first three lumbar nerves are directed strongly caudad (as well as
ventrad), so that on leaving the intervertebral foramen they pass
ventrad of the transverse process of the vertebra immediately
succeeding. Each communicates with the sympathetic system and gives off
near its origin branches to the muscles on the ventral side of the
vertebræ,--the first to the crus of the diaphragm, the second and third
(Fig. 162, _II_ and _III_) to the quadratus lumborum and psoas muscles.
Each divides three to five centimeters from its origin into a =lateral=
and a =medial= branch, the first having a more cranial, the latter a
more caudal course. The first three nerves of the cat are represented in
man by the iliohypogastric and the ilioinguinal nerves. There seems no
good ground for applying these names to two of the three in the cat, in
preference to the third, so that we shall speak of these nerves in the
cat as simply the first, second, and third lumbar nerves.
1. The first lumbar nerve arises from the intervertebral foramen caudad
of the first lumbar vertebra. Its lateral division passes between the
transversus and obliquus internus muscles, then between the obliquus
internus and externus. At about the middle of the abdomen it pierces the
obliquus externus and is distributed to the integument of the middle of
the ventral surface of the abdomen. The medial division passes between
the obliquus internus and transversus, crosses the lateral division of
the second (lying mediad of it), and extends to the rectus abdominis,
which it supplies.
2. The second lumbar nerve (Fig. 162, _a_) divides, like the others,
into two branches. The lateral branch pierces the muscles of the
abdominal wall at the lateral border of the longissimus dorsi and
passes, lying just beneath the integument, ventrocaudad nearly to the
pubis. It supplies the integument of the caudal half of the abdomen and
of the fold between the thigh and abdomen. The medial branch passes at
first almost directly caudad, lying on the medial surface of the
transversus abdominis; it curves gradually ventrad, lying in the
substance of the transversus, and reaches the rectus abdominis three or
four centimeters craniad of the pubis.
3. The third lumbar nerve (_b_) is not united with the fourth, as in
many animals, but remains distinct. It divides one or two centimeters
from its origin. The lateral branch passes caudad to the outer surface
of the abdominal muscles, and extends, lying just beneath the
integument, to that portion of the abdominal wall which is partly
covered by the thigh. The medial branch passes caudad on the lateral
surface of the iliopsoas muscle, follows the iliolumbar artery for a
short distance, and gives branches to the caudal part of the transversus
and rectus abdominis muscles.
=The Lumbar Plexus= (Fig. 162).--The fourth, fifth, sixth, and seventh
lumbar nerves are interconnected by short branches, forming thus the
=lumbar plexus=. They are also connected with the sacral plexus, so that
the two are often considered together as the =lumbosacral plexus= (Fig.
162). In some other animals the first three lumbar nerves form also a
part of the plexus; but they are not connected with it in the cat.
The fourth lumbar nerve forms the genitofemoral (_c_) and part of the
lateral cutaneous (_d_) nerves, and is connected by a short strand with
the fifth. The fifth aids in forming the lateral cutaneous (_d_) and
femoral (_f_) nerves, and is connected by a short branch with the sixth.
The sixth lumbar is large; it forms the major part of the femoral (_f_)
and a large part of the obturator nerve (_g_), and sends a large
connecting branch caudad to join the seventh and thus pass into the
sacral plexus. The seventh passes caudad to join the sacral plexus and
aid in forming the great sciatic nerve (_h_); by its connection with the
sixth it aids in forming also the obturator nerve (_g_).
4. =N. genitofemoralis= (or N. lumboinguinalis) (_c_, _c′_, _c″_).--This
is a direct continuation of the fourth lumbar nerve. Its medial branch
(_c″_) passes along the medial surface of the iliopsoas (8) and the
psoas minor (9) to the external iliac artery, accompanies this, lying on
the ventral surface, from its origin to the point where it gives off the
profunda femoris, then accompanies the latter artery and passes onto
that branch of it that spreads out under the integument of the ventral
pelvic region. It crosses the spermatic cord and ramifies in the skin of
the proximal part of the medial side of the thigh. The lateral branch of
the genitofemoralis (_c′_) pierces the psoas minor (9), appearing on its
ventral surface opposite the fifth lumbar vertebra. It passes caudad on
the ventral surface of this muscle, crosses the iliolumbar artery, then
turns caudolaterad, passes through the abdominal wall, and is
distributed to the craniomedial surface of the thigh and to the adjacent
abdominal wall.
This nerve is variable in origin and in distribution. Its lateral branch
is sometimes lacking.
5. =N. cutaneus femoris lateralis= (_d_).--The lateral cutaneous nerve
arises from the connecting strand between the fourth and fifth nerves,
most of its fibres coming from the fifth. It passes caudoventrad between
the iliopsoas and psoas minor and accompanies the iliolumbar artery
across the ventral surface of the iliopsoas. It pierces the abdominal
wall in company with the artery and passes onto the cranial border of
the thigh. Its terminal branches are distributed to the integument along
with the branches of the iliolumbar artery,--supplying the lateral
surface of the femur and extending as far as the knee.
6. =N. femoralis= (_f_).--The femoral is a large nerve which rises by
strong roots from the fifth and sixth lumbar nerves. It gives branches
to the iliopsoas (8) and passes through that muscle to its ventral
surface. It leaves the abdominal cavity lying on the ventral surface of
the iliopsoas, and at the point where it pierces the abdominal wall it
divides into three (or four) branches. One (or two) of these pass to the
sartorius muscle. Another passes between the rectus femoris and vastus
medialis muscles, and divides into numerous branches which supply these
muscles and the vastus intermedius.
The third branch of the femoral is =N. saphenus= or the =long saphenous=
nerve (Fig. 127, _g_, page 310). This passes distad along with the
femoral artery and vein, giving a few twigs to the integument. Where the
long saphenous artery (_f_) separates from the femoral artery the nerve
follows the former and passes with it along the medial side of the lower
leg. At the knee and in the lower leg it gives off a number of cutaneous
branches, and finally divides just distad of the middle of the lower leg
into two main branches. Both of these pass to the concavity of the
ankle-joint and divide into fine branches, which form a sort of plexus
on the ankle and dorsal surface of the foot; branches from this can be
traced almost to the toes.
7. =N. obturatorius= (Fig. 162, _g_).--The obturator nerve arises from
the connecting band between the sixth and seventh nerves. It lies at
first laterad, then dorsad, of the common iliac vein, and passes almost
directly caudad to the cranial border of M. obturator internus (15).
Here it turns sharply laterad about the pubis, and passes through the
obturator foramen. It gives twigs to the obturator externus muscle, and
divides into several branches, which innervate the adductor femoris,
adductor longus, pectineus, and gracilis.
[Illustration: FIG. 162.--THE LUMBAR AND SACRAL NERVES, AS SEEN IN A
VIEW OF THE DORSAL WALL OF THE ABDOMINAL CAVITY, AFTER REMOVAL OF THE
VISCERA.
On the right side the iliopsoas, psoas minor, and quadratus lumborum
have been removed. The symphysis pubis has been split and the two
parts divaricated, to show the pelvic cavity; on the right side parts
of the innominate bones and the levator ani and coccygeus muscles have
been removed. _II-VII_, second to seventh lumbar nerves; 1-3, first to
third sacral nerves. _a_, second lumbar nerve; _b_, lateral and medial
branches of third lumbar nerve; _c_, N. genitofemoralis (_c′_, its
lateral branch; _c″_, its medial branch); _d_, N. cutaneus femoralis
lateralis; _e_, muscular branch of N. femoralis; _f_, N. femoralis;
_g_, N. obturatorius; _h_, N. ischiadicus or great sciatic nerve; _i_,
N. gluteus superior; _j_, N. gluteus inferior; _k_, N. cutaneus
femoris posterior; _l_, N. pudendus; _m_, N. hemorrhoidalis inferior;
_n_, part of the sympathetic (incompletely shown, merely to indicate
connections with the spinal nerves); 4, M. transversus abdominis; 5,
6, cut edges of M. obliquus internus and externus; 7, dorsal border of
the diaphragm; 8, M. iliopsoas (mostly removed on the right side); 9,
M. psoas minor; 10, M. pyriformis; 11, M. levator ani; 11′, M.
iliocaudalis; 12, M. flexor caudæ longus; 13, M. flexor caudæ brevis;
14, edge of pubic symphysis; 15, cut end of M. obturator internus; 16,
cut ramus of ischium; 17, cut ramus of pubis.]
D. SACRAL NERVES AND SACRAL PLEXUS (Fig. 162).--A large band passes
caudad from the sixth and seventh lumbar nerves to connect with the
sacral nerves; this constitutes the so-called =lumbosacral cord=. The
sacral nerves are three in number. Their dorsal rami pass dorsad out of
the two posterior sacral foramina and the foramen caudad of the sacrum,
to the muscles and skin dorsad of the sacrum. The ventral rami pass from
the two anterior sacral foramina and from the foramen between the last
sacral and first caudal vertebræ. The first is the largest; it joins
the lumbosacral cord to form the great sciatic nerve (N. ischiadicus)
(_h_) and the superior (_i_) and inferior (_j_) gluteal, and sends a
branch caudad to connect with the second sacral. The second and third
sacral nerves are small; they unite with the connecting branch from the
first to form a network from which arises the pudendus (_l_), cutaneus
femoris posterior (_k_), hemorrhoidalis inferior (_m_), and a small
branch to the great sciatic (_h_).
The nerves arising from the sacral plexus are the following:
1. =N. gluteus superior= (Fig. 162, _i_; Fig. 163, _j_).--The superior
gluteal nerve arises from the lumbosacral cord and the first sacral
nerve; it passes dorsad in the notch between sacrum and ilium,
caudolaterad of the first anterior sacral foramen, curves over the
dorsal border of the ilium between the gluteus medius and pyriformis
muscles (Fig. 163, 7), passes between the gemellus superior (6) and
gluteus minimus (5) and ventrad of the latter, and reaches the medial
surface of the tensor fasciæ latæ, which it innervates. In its course it
sends branches to the gluteus medius, gluteus minimus (5), and gemellus
superior.
2. =N. gluteus inferior= (Fig. 162, _j_; Fig. 163, _i_).--A small nerve
from the lumbosacral cord and the first sacral nerve. It passes
dorsocaudad, lying on the dorsal surface of the great sciatic nerve
(Fig. 162, _h_). After leaving the pelvis by the great sciatic notch it
divides beneath the pyriformis (Fig. 163, 7) into two branches; one goes
to M. caudofemoralis (4), the other to M. gluteus maximus (3).
3. =N. ischiadicus= (Fig. 162, _h_; Fig. 163, _a_).--The =great sciatic=
nerve, the largest nerve in the body, arises from the lumbosacral cord
(formed chiefly by the sixth and seventh lumbar nerves), the first
sacral nerve and a small branch from the second sacral. It passes
caudodorsad and leaves the pelvis by passing across the great sciatic
notch, between M. pyriformis and M. gemellus superior. It passes across
the tendon of M. obturator internus (Fig. 163, 9) near the insertion,
and here sends caudad a large muscular branch (_b_) beneath the biceps.
This branch innervates the biceps, semitendinosus (17) and
semimembranosus (16). Other twigs in this region pass to the quadratus
femoris (10) and tenuissimus. The great sciatic nerve (_a_) now passes
across the quadratus femoris (10), adductor femoris (15), and
semimembranosus (16), lying beneath the biceps femoris. It thus enters
the popliteal space and approaches the popliteal artery and vein. Here
it gives off one or two small muscular branches to the distal part of
the biceps, and sends a slender branch, =N. suralis= (_c_), along the
medial surface of the biceps to the lateral surface of the lateral head
of M. gastrocnemius (20). The sural nerve (_c_) becomes cutaneous at the
distal (ventral) border of the biceps, and divides three or four
centimeters proximad of the ankle into two branches. One passes over the
tendon of Achilles (27) to the proximal end of the calcaneus and
ramifies in this region. The other passes onto the lateral surface of
the foot, and supplies the integument in this region over the tarsus and
part of the metatarsus.
The great sciatic nerve now divides in the popliteal space into the
=peroneus communis= (_d_) and the =tibialis= (_e_).
[Illustration: FIG. 163.--DISSECTION OF LEG, LATERAL VIEW, TO SHOW
DISTRIBUTION OF THE GREAT SCIATIC NERVE.
The biceps, caudofemoralis, gluteus maximus, gluteus medius, tensor
vaginæ femoris, and part of the peroneus longus have been removed.
_a_, N. ischiadicus or great sciatic nerve; _b_, muscular branch; _c_,
N. suralis; _d_, N. peroneus communis; _e_, N. tibialis; _f_, N.
peroneus profundus; _g_, N. peroneus superficialis and its terminal
branches; _h_, branches of N. cutaneus femoris posterior; _i_, N.
gluteus inferior; _j_, N. gluteus superior; _k_, vena saphena parva;
_k′_, communicating branch to V. glutea inferior. 1, M. sartorius; 2,
cut origin of M. gluteus medius; 3, cut origin of M. gluteus maximus;
4, cut origin of M. caudofemoralis; 5, M. gluteus minimus; 6, M.
gemellus superior; 7, M. pyriformis; 8, M. flexor caudæ longus; 9, M.
obturator internus; 10, M. quadratus femoris; 11, tuberosity of the
ischium; 12, great trochanter of femur; 13, M. rectus femoris; 14, M.
vastus lateralis; 15, M. adductor femoris; 16, M. semimembranosus; 17,
M. semitendinosus (the slender ribbon-like muscle crossing this is M.
tenuissimus); 18, M. vastus intermedius; 19, M. plantaris; 20, M.
gastrocnemius; 21, M. peroneus longus (cut); 22, M. tibialis anterior;
23, M. extensor longus digitorum; 24, transverse ligament; 25, M.
peroneus brevis; 26, M. soleus; 27, tendon of Achilles; 28, M.
extensor brevis digitorum; 29, tendon of M. peroneus tertius.]
_a._ =N. peroneus communis= (_d_).--This is the more lateral of the two
divisions of the great sciatic nerve. It passes along the medial surface
of the biceps to the lateral surface of the lateral head of M.
gastrocnemius (20), where it extends to a point just distad of the head
of the fibula. Here it passes beneath that part of the gastrocnemius
which has origin on the fascia of the shank, passes between the soleus
and peroneus longus (21), then between the peroneus longus and peroneus
tertius. It gives off a number of small muscular branches, then divides
two or three centimeters distad of the head of the fibula into two main
branches, =N. peroneus superficialis= (_g_) and =N. peroneus profundus=
(_f_).
(1) =N. peroneus superficialis= (_g_).--The superficial peroneal nerve
passes distad between the peroneus longus and peroneus tertius. Near the
ankle it becomes superficial, passing along the concavity of the ankle
across the transverse ligament which binds down the tendons of the
extensor longus (23) and tibialis anterior (22), and thus reaches the
dorsal side of the foot. Two or three minute twigs are given off to the
ankle, then the nerve divides into four divisions. These pass distad to
the toes, subdividing so as to send a nerve to each side of each toe.
(2) =N. peroneus profundus= (_f_).--The deep peroneal nerve passes
between the tibialis anterior and extensor longus digitorum muscles,
gives branches to these muscles, and passes distad with the tibialis
anterior artery, lying on the inner surface of the tibialis anterior
muscle. It passes onto the dorsum of the foot, lying on the inner
surface of the tendon of the muscle. On the tarsus it divides into two
branches. The lateral branch passes into the extensor brevis digitorum,
while the medial one extends in the dorsal groove between metatarsals
four and five to the toes; here it divides into two nerves which supply
the contiguous sides of digits four and five.
_b._ =N. tibialis= (_e_).--The tibial nerve passes distad parallel with
the peroneal nerve, but mediad of it. It passes between the lateral and
medial heads of the gastrocnemius, giving off muscular branches to
these, and to the plantaris and soleus. It then passes between the
plantaris and the medial head of the gastrocnemius, and reaches the
space between the plantaris and flexor longus hallucis, where it passes
distad. It gives off, in the region just described, muscular branches to
the flexor longus digitorum, flexor longus hallucis, and tibialis
posterior. Below the middle of the lower leg the nerve becomes
superficial (Fig. 127, _i_, page 310), lying on the ventral surface of
the flexor longus hallucis. It passes in the depression between the heel
and the medial malleolus onto the plantar surface of the tarsus, sends a
small branch to the plantar surface of the heel, and divides into two
branches, the =medial= and the =lateral plantar= nerves.
(1) =N. plantaris medialis.=--The medial plantar nerve passes along the
medial border of the flexor brevis digitorum and divides into two
branches. One passes to the medial (second) digit, supplying both sides;
the other supplies the third digit in the same way. Both send branches
to the fibrous pad on the sole of the foot.
(2) =N. plantaris lateralis.=--The lateral plantar nerve passes laterad
across the tendon of the flexor longus digitorum to its lateral edge. At
about the proximal end of the metatarsi it divides into two branches.
The lateral branch passes distad to the ventral surface of the fifth
digit. The medial branch passes beneath the tendon of the flexor longus
digitorum and transversely across the interossei; it divides into
numerous tendons which innervate the interossei and other short muscles
of the sole of the foot.
4. =N. pudendus= (Fig. 162, _l_; Fig. 112, 8, page 265).--This arises
(Fig. 162, _l_) from the sacral plexus caudad of the great sciatic
nerve. It has two roots, one from the second sacral, one from the third,
and it may also receive a small accession from the great sciatic nerve
(_h_) three or four centimeters caudad of the origin of the latter. It
passes at first dorsolaterad, laterad of the coccygeus muscle, then
curves mediad toward the anus. It divides into two branches: one passes
to the base of the penis, sends twigs into the compressor urethræ
muscle, and passes onto the dorsal surface of the penis. This branch is
=N. dorsalis penis=; it extends with the artery of the same name to the
glans. The second branch of N. pudendus (=N. hemorrhoidalis medius=)
passes to the anus and innervates the muscles and other structures about
the caudal end of the rectum. In the female, branches of N. pudendus
supply the urogenital sinus and adjacent structures (Fig. 112, 8).
5. =N. cutaneus femoris posterior= (Fig. 162, _k_; Fig. 163, _h_).--This
arises from the sacral plexus, its roots coming chiefly from the second
and third sacral nerves, and passes caudodorsad, at first in close
connection with N. pudendus. It then accompanies the posterior gluteal
artery and vein, sends branches (perineal nerves) into the fat at the
sides of the anus, and branches onto the lateral surface of the biceps
muscle. One of the latter follows the communicating vein (Fig. 163,
_k′_) from V. saphena parva, and may be traced as far distad as the
popliteal space.
6. =N. hemorrhoidalis inferior= (or =posterior=) (Fig. 162, _m_).--This
arises by two roots, from the second and third sacral nerves, and passes
with the inferior hemorrhoidal artery ventrad across the lateral surface
of the rectum to the urethra. Here it divides into two parts: one passes
craniad to the bladder, the other caudad onto the ventrolateral surface
of the rectum.
A small nerve passes from the sacral plexus, especially from the third
sacral nerve, into M. levator ani (Fig. 162, 11). Another small nerve
from the same region passes to M. coccygeus, and a third to the proximal
end of M. tenuissimus.
E. NERVES OF THE TAIL. COCCYGEAL NERVES.--From the intervertebral
foramina of the first seven or eight caudal vertebræ spinal nerves of
the usual type are given off. The dorsal rami innervate the dorsal
muscles of the tail. The ventral rami are interconnected with each other
and with the last sacral nerve by a longitudinal cord; they innervate
the muscles and integument of the ventral side of the tail.